Typical sinks, in bathrooms for example, contain an opening near the top of the bowl that overflow water can drain into and an opening at the bottom of the sink as the main drain hole. Typically a channel is cast as part of the sink that takes the overflow water from the sink opening near the top to the main drain at the bottom of the sink. The sink casting includes the passage for the drain at the bottom of the sink. At the bottom of the sink, the casting flares out to provide support and leak protection.
A drain is placed in the main drain hole to direct the water into the pipe which carries the water away. There are many types of drains that can be placed in the drain hole at the bottom of the sink. For example, the grid drain has been used in lavatories (bathroom sinks) for decades.
A common grid drain is a solid casting, such as brass, having a top surface. The surface typically contains 19 holes that are in a six sided pattern. Each hole is the same diameter (5 mm) and the hole spacing is equidistant in each direction. The casting is approximately 6.5 cm long. From the bottom, the external side is threaded up about 2.4 mm. The internal area is fine machine threaded to accept a tail piece of varying length. Above the external threading are two openings of non-critical length and width. The openings are primarily used for overflow water drainage from the sink.
Thus, the typical bathroom sink is configured with an overflow opening and a drainage channel which connects to a chamber at the bottom of the sink. The standard drain is inserted into this chamber, with the bottom and top sealed to prevent leakage.
There is a growing demand for regular sinks not to have the overflow channel. For example, the Canadian Product Certification Board (CSA) has requested that all sinks in hospitals and other high risk infection areas have sinks without the overflow channel. There appears to be medical evidence that bacteria, germs, etc. can grow in these channels. In addition, there is a demand for stainless steel sinks in certain bathroom configurations. These are designed without overflows and with no bottom chamber.
In order to attach a grid drain to a sink without an overflow channel, there needs to be external threading all the way up to the bottom of the flange. There cannot be any openings in the side of the drain. Otherwise, water will spill out on the floor.
In response, the current grid drain was modified by not cutting an overflow hole but instead providing external threads up to the flange. This arrangement allows the drain to be installed without leaking. However, if sufficient water flows on to the top of the drain, an air bubble will form directly under the top flange, inside the drain. This is called the "venturi effect." The flowing water over the top of the drain causes low pressure to form in the drain. This manifests itself into an air bubble. This air bubble effectively blocks the drain. Water will build up in the sink and could eventually spill out. Until the air bubble dissipates, water is blocked from the drain.
In a conventional sink with an overflow chamber, the air bubble dissipates up the channel whenever it forms. The overflow chamber channel acts as a vent or a pressure equalizer. Thus, without pressure equalization, air bubbles will form on the underside of the grid drain. The air bubbles block the drain from releasing sufficient water from the sink to avoid overflow of the water.
There is a need for an effective grid drain that can be used without an overflow chamber.